Visit Settings → Email → Snippets (/settings/me/email/snippets). Each snippet has a name (e.g., “Intro paragraph”), a shortcut (e.g., intro), and a body (HTML allowed). Pick a scope: Just me for a private snippet, or Whole org to share with the team.

• Shortcuts are 1 to 32 chars, lowercase letters + digits + _ + -.
• Body is up to 16,000 chars; can include simple HTML formatting.
• Org-shared snippets show with an “Org-shared” tag in the list.

In the message you are writing, in the compose window or in a reply under an email, type ; followed by the shortcut and a trailing space (or Enter / Tab). The trigger replaces with the snippet's body and leaves your cursor at the end. The trigger character must be at the start of the line, after whitespace, or after punctuation. Emoticons like ;) stay safe.